FGD and DeNOx
NEWSLETTER       

February 2011
No. 394

ROFA and Rotamix at Elektrownia Opole

Nalco Mobotec’s Rotating Opposed Fired Air (ROFA^®) and Rotamix^® and extensive windbox modifications were installed at PGE’s Elektrownia Opole Unit 3 in Poland to reduce NO_x emission.  The RAFAKO BP-1150 boiler is a 380-MW tangentially-fired tower boiler. The installation included three steps:  (1) An operational, mechanical and performance review of the existing firing system, leading to tangential windbox modification and upgrade, (2) the existing SOFA system was replaced by Nalco Mobotec’s ROFA system, and (3) a Rotamix SNCR system was installed, introducing urea into the upper furnace.

In 2016, Polish NO_x emissions regulations are to drop to 200 mg/Nm³ (at 6 percent O₂) under the large combustion plant directive (LCPD). Due to the large number of boilers in Poland that must be below 200 mg/Nm³, many are installing equipment early. In 2008, PGE Elektrownia Opole procured the Mobotec System.

Elektrownia Opole mandated that the installation could not degrade plant performance with specifications on CO, flyash LOI, slag ash LOI, ammonia slip, ammonia in ash, ammonia in gypsum, ambient noise, availability, boiler efficiency, wastage, steam flow, steam temperature, and consumption of urea, water, electricity and compressed air.

To maximize SNCR efficiency, it is important to minimize CO in the upper furnace. Improved fuel/air mixing in the burner zone facilities CO burnout. Nalco Mobotec felt that having automated secondary air (SA) nozzle tilt control for superheat (SH) and reheat (RH) temperature along with the existing attemperation system was beneficial for the project. Drives were added to control the tilts for all three independent vertical burners groups. The CCOFA ports were replaced with new higher velocity nozzles and were also provided manual control for both tilt (vertical) and yaw (horizontal). Also, the lower secondary air nozzles in each corner were modified with a Lower Furnace CO Control (LFCC) system. As part of the windbox modifications, the SA nozzles located between pairs of burners were replaced with new nozzles to increase exit velocity and windbox pressure control.

The windbox SA flow dampers were also modified to provide operation with increased air biasing control. The downstream dampers were modified and entry loss optimized by adding a venture-shaped entry. A portion of the secondary flow control dampers (all but coal nozzle secondary air feed) were equipped with modulated actuators to improve control of flow and windbox pressure across load. RV Industries designed and supplied the tangential-firing system components, including installations and startup support.

The Rotamix system consists of an air delivery system and a liquid (urea and water) delivery system. The air delivery system contains a small ambient-air fan and ductwork similar to the ROFA system, but smaller in size. There are several levels of Rotamix ports; including ports between gaps in the radiant wall superheater bands and ports in the upper furnace between SH platens. Urea can also be injected through the ROFA nozzles. The upper furnace injection ports have injection angle adjustment capability. In addition to the diluted urea, Rotamix humidification water is delivered to any injection device that is in service. The humidification water system adds additional control and tuning capability to the Rotamix system as urea injection concentrations can be manipulated to compensate for furnace flow anomalies.

Brian Higgins, Baiyun Gong, Ed Pozzobon and Guisu Liu of Nalco Mobotec; Edward Kinal, Jan Pilipionek and Miroslaw Pietrzyk of Elektrownia Opole and Robert Zmuda, Peter Hajewski and Wlodzimierz Blasiak of Nalco Mobotec Polska reported at Power-Gen 2010 that the combined effect of burner modification and the ROFA and Rotamix systems resulted in:

(1) NO_x emission below 200 mg/Nm³, averaging 168 mg/Nm³ (52 to 66 percent reduction).

(2) Demonstrated ability to handle significant fuel variability.

(3) Improved combustion due to mixing introduced by the ROFA system. O₂ is reduced in the furnace, lowering NO_x and improving boiler efficiency.

(4) LOI for flyash averaged 3.5 percent, which is below the limit for continued flyash sales.

(5) LOI for slag ash averaged 7.3 percent, which is high, but will be managed through tuning.

(6) CO emissions were held to an average value of only 41 mg/Nm³ over the ten days testing.

(7) Ammonia slip from the SNCR system was held to 3.1 ppm on average and below 5 ppm for full load conditions. 

(8) Ammonia in ash averaged 35 mg/kg (below the 50 mg/kg limit).

(9) Ammonia in gypsum averaged 8.6 mg/kg (below the 10 mg/kg limit).8

(10) The FD and ID fan power usage dropped by a total of 830 kW, or 10 percent. This savings nearly made up for the entire power usage required for the ROFA fan. The net power increase post-ROFA installation was two percent of the total parasitic fan load and less than 0.05 percent of the produced power.

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